unexplained brake noise

[amplifire]

I'm wondering if anyone has any insight into this: My rear brakes have been making some noise for a few months, so I thought it was probably due for some new pads. Only thing that had me concerned is that it isn't the typical squealing or grinding, but more of a "catching" sound that isn't constant but varies with the rotation of the wheel. I took it into a dealership to have it looked at, they said that the pads themselves were still at 6mm so have life left, but that there was alot of brake dust build-up that the tech believed was causing the noise. So I let them clean it out and re-finish the drums, but of course when they were done the noise was unchanged. Then they spent some time trying to figure out what was making the noise, inspected each component, and everything is apparently in perfect condition. They used the chassis ears and pinpointed the sound to be loudest from the backing plate of the brake assembly, but since all parts appear fine, can't do anything about it. At this point they returned my keys and I drove away. I'm glad to know that the brakes are in good working order, but I can't help feeling uneasy, as I don't understand how it would be making this noise without something being wrong in there... Any ideas or similar experience?

[Snafu]

Did they check the rear wheel bearings and how is the rear diff fluid level?

[amplifire]

they didn't say anything about checking the bearings, so I would guess they didn't... I haven't checked the diff fluid level, but I have a bunch of new fluid in the basement as I was planning on changing it today but it's raining here and I am garage-less so it'll have to wait. I hadn't suspected the bearings because it only happens when I apply the brake, not sure if that is a good assumption though. I was just searching XOC on this, best I can find it some people that have had the pads not put on correctly or had slipped from the proper position; the tech had it all apart so I would guess he'd have put it back together properly, I guess there is no guarantees on that though

[Snafu]

Oops. Didn't read that part about the noise only happening when you brake. If so then I wouldn't suspect the bearings.

[amplifire]

Sorry, forgot to mention that in the original post

[Fade_2_Black]

Possibly a loose backing plate?

[Simon]

That's possible. Could also just be the type of pads that are on there. Some are noisier than others. Also, if they've gotten really warm, they could have a glaze on them.

[Morpheus]

That's possible. Could also just be the type of pads that are on there. Some are noisier than others. Also, if they've gotten really warm, they could have a glaze on them.

I'm sure they would have deglazed them when they serviced the brakes. I've seen rotors make noise, even when they look fine. (or drums in this case)

[amplifire]

so I guess I should just ignore it until it's time to replace the drum? I was going to take it apart and start poking around in there myself, but I don't really know what it's supposed to look like so I don't think I'd see anything that the tech wouldn't. Thanks for the replies everyone.